/Engine/Source/Runtime/Engine/Classes/Particles/ParticleSystemComponent.h
Particle event data for particles that already existed at the time of the event
struct FParticleExistingData : public [FParticleEventData](API\Runtime\Engine\Particles\FParticleEventData)
FVector
Direction
The direction of the particle at the time of the event.
float
ParticleTime
How long the particle had been alive at the time of the event.